Predation (with parsitism and herbivory)

When one animal (a predator) eats (and kills) another animal (a prey), the predator clearly benefits (+) and the prey is harmed (-).

When one animal feeds from the body of another (the host) without killing it, the interaction is called parasitism. The parasite benefits (+) and the host is harmed (-).When an animal consumes plant material, the interaction is called herbivory. The herbivore benefits (+) and we normally assume that the plant is harmed (-).

Now think about these interactions in evolutionary terms. The species that is harmed is under more-or-less severe selective pressure to minimize the harm.

There are an enormous variety of defensive adaptations in both animals and plants. Here are a few examples from the plant world:

Plants can’t run and hide, so most of their defenses are either structural or chemical. The more interesting ones are chemical…

1.Do you like chocolate? What gives chocolate much of its flavor is an alkaloid (a toxin) that’s

present to protect the beans from insect herbivores.

2.Do you like cinnamon? It comes from the bark of a tree. The ‘flavor’ is a toxin (here cinnamic acid) again present to protect the bark from insect herbivores.

3. Let’s save time an space. Virtually every strong flavor we like (pepper – capsicic acid, …) has evolved in the plant source for protection from insects.

And the structural defenses are fairly obvious…

Thorns, hooks, spikes, or prickles in plants and spines (porcupine quills) in animals, e.g. cactus

In animals there is a greater variety of approaches to defense.

1.Warn a potential predator that you’re dangerous (or even poisonous).It’s called aposematic coloration

The warning colours are generally stripes of red and/or yellow contrasted with black. All 3 colors are seen in coral snakes; yellow and black are in bees and wasps.

2. Crypsis (or camouflage) – hiding in plain sight. Think of other examples like stick insects or insects with leaf-like wings, …

Against an artificial background

In its natural habitat

3. Mimicry – if you can’t hide, try looking like something the predator wouldn’t want to eat. There are two kinds of mimicry: Batesian, where the mimic tastes good, and the model is distasteful, or Mullerian, where both model and mimic are distasteful.

Batesian mimicry

Hawkmoth – leftSnake - right

Probably the most famous example of Batesian mimicry is the Monarch (model) and Viceroy (mimic) butterflies…

The Viceroy is not distasteful (it may even taste good)

The Monarch is distasteful, even causing bird predators to vomit.

Blue jay vomiting after eating a noxious monarch butterfly. The caterpiller obtains poison from its milkweed host plant.

Photo: Lincoln P. Brower, Univ. of Florida

In Müllerian mimicry 2 different species resemble each other, e.g., wasps & bees are both black & yellow. The advantage to the prey is that predators are quick to learn to avoid both species.

The modela hornet

A beetlemimic

fly

moth

Deceptive colouration - eyespots attract predators toattack places on the body that do not result in fatality. The eyespots are intended to make the prey look like a frightening predator.

They may also have displays that at least momentarilyfrighten a predator.

Animals may adopt chemical defenses, too.

Some molluscs secrete sulfuric acid, and are rejected as food by fish

A number of animals use defensive sprays. Whip scorpions (related to spiders) spray acid.

Skunks spray a concentrated musk (mercaptan) that we can all agree is effective in defense against attack.

Dendrotoxin (which blocks potassium channels in the predator’s nerve cells) is in the skin of certain poisonous frogs, and used by hunters in the Amazon rainforest.

Tetrodotoxin (used in neurophysiological research) comes from the puffer fish. It blocks sodium channels.